Solar energy that reaches the earth includes wavelengths of about 300 nanometers (nm) to about 2500 nm. About 5% of this energy is in the ultraviolet range (about 300 nm to about 400 nm). About 46% of the total energy of the sun is in the visible spectrum (about 400 nm to about 780 nm), and the remaining about 49% is in the infrared range (about 780 nm to about 2500 nm). Radiation in this region may be invisible but can still be perceived as heat. Untreated glass is typically transparent to infrared radiation, and consequently infrared radiation from sunlight transmitted through a window may result in significant heat gain within a building or other enclosure. Additionally, ultraviolet radiation may also penetrate a glass window and may be converted to infrared radiation within the enclosure due to greenhouse effects. In order to maintain room habitability, cooling systems, such as HVAC systems, may be used to counter the increased heat due to the infrared radiation build-up. In regions with high insulation, significant costs may be associated with air conditioning required to counteract the amount of room heat derived from window-transmitted solar energy.
Frequently, darkly tinted or reflective window coatings have been used to block infrared radiation entering through a glass window. However, such coatings may substantially reduce the amount of normal visible light, and may, therefore, alter or distort the outside view by a room's occupants.
Thus, there is a need for a low cost and environmentally friendly coating that can be applied to glass or incorporated during glass manufacturing that can reflect heat but still permit high transmission of visible light.